1. Field of the Invention
The present invention relates to an automatic document feeder attached to a copying apparatus and the like, and automatically setting documents in a predetermined position. More specifically, the invention relates to an automatic document feeder for conveying documents by means of a conveyer delivery belt.
2. Description of the Prior Art
There has been known an automatic document feeder including a function to convey documents by means of a delivery belt.
When setting a document, the automatic document feeder of this type is adapted to control timing to drive or to brake the delivery belt so as to set the document with its leading or trailing edge placed on the reference line.
However, there is a drawback that if the delivery belt is merely braked at a predetermined timing, a halt position shifts according to various sizes of the document.
There is also known a document feeder adopting a method, wherein for the purpose of setting the trailing edge of the document more accurately on the reference line, the document runs a little bit over a setting position, and then the delivery belt is reversed to switch back the document and to make the document edge bump against a protruded portion disposed on the reference line.
With this method, however, the document edge bumps against the protruded portion for positioning and therefore, the document is apt to suffer damages such as edge bending.
This is because when the delivery belt conveys the document, a contact ratio of the delivery belt to the conveyance path surface, e.g. contact glass, varies according to size or kinds of the document.
Normally, the surface of the delivery belt is made rough to give a large friction coefficient. Accordingly, in the case of carrying small sized documents, a large force for driving the delivery belt is required because the contact area of the delivery belt to the conveyance path surface is large. As opposed to this, the larger the document conveyed, the smaller the contact area of delivery belt to the conveyance path surface, requiring the smaller driving force. Thus, various sizes of the document lead to varying the load on a driving means for driving the delivery belt, such as a motor.
In the same way, different kinds of documents, in terms of paper quality or thickness for example, will also lead to varying the load on the driving means for the delivery belt.
That is, the larger the document is, the further the document is conveyed to halt beyond the halt position and hence, the document cannot be set accurately in a predetermined position.